Neurodegenerative diseases are becoming more prevalent with the aging population. One particular neurodegenerative disease which typically has its onset between the ages of 50 and 80 years of age is Parkinson's disease. Parkinson's disease is a disorder of the brain which is characterized by tremor and difficulty with walking, movement, and coordination.
Parkinson's disease appears to be caused by a progressive deterioration of dopamine-containing neurons in the substantia nigra zona compacta of the brain. Dopamine is a chemical neurotransmitter which is utilized by brain cells to transmit impulses to control or modulate peripheral muscle movement. The loss of the dopamine-containing neurons results in reduced amounts of dopamine available to the body. Insufficient dopamine is thought to disturb the balance between dopamine and other neurotransmitters such as acetylcholine. When such dopamine levels are reduced, nerve cells cannot properly transmit impulses, resulting in a loss of muscle control and function.
Currently, there is no known cure for Parkinson's disease. Treatments are typically aimed at controlling the symptoms of Parkinson's disease, primarily by replacing the dopamine, with either L-DOPA which is metabolized to dopamine, or by administering chemical agents that stimulate dopamine receptors. Current treatments to slow the progression of the disease include compounds such as deprenyl (Selegeline), a selective monoamine oxidase inhibitor, and amantadine, a compound that appears to decrease dopamine uptake into presynaptic neurons.
Certain hydroxylated (mono-phenolic or catechols) phenylethylamines (as such or forming part of a semi-rigid/rigid ring system) are known to have useful dopaminergic activity. However, their clinical use is limited because they have low or no bioavailability (high first-pass effect).
It has been reported that (±)-5-keto-2-N,N-di-n-propylamino-tetrahydrotetralin ((±)-5-keto-DPATT (Formula A)) does possess dopaminergic effects in rats in vivo. However, in vitro binding of this compound does not take place, i.e. (±)-5-keto-DPATT has itself no affinity to DA receptors. Consequently, it must be bioactivated before displaying its effects. This was published on a poster by Steven Johnson at a local Med. Chem. Meeting in Ann Arbor, Mich., USA in 1994. There was no mentioning of catecholamine formation on that poster. However, it was speculated, but not shown, that the active drug may be (±)-5-OH-DPAT (see Formula B below). Consequently, the compound of Formula II, falling within the generally claimed structure of Formula I, is provisoed from the present invention. 
In recent years a large body of pharmacological, biochemical and electrophysiological evidence has provided considerable support in favor of the existence of a specific population of central autoregulatory dopamine (DA receptors) located in the dopaminergic neuron itself and belonging to the D2 receptor subclass of DA receptors. These receptors are part of a homeostatic mechanism that modulates nerve impulse flow and transmitter synthesis and regulates the amount of DA released from the nerve endings. Recently, Sokoloff, et al., Nature, 347 146–51 (1990) presented evidence for the existence of a new type of dopamine receptor called D3. In a series of screened classical and a typical neuroleptics, the preferential dopamine autoreceptor antagonists (+)-AJ76 and (+)-UH232 possessed the highest preference for the D3 site. The D3 receptor appears to occur both pre- and postsynaptically, and the regional distribution (high preference in limbic brain areas) differs from that of the D1 and D2 receptors.
Drugs acting as agonists or antagonists on central DA transmission are clinically effective in treating a variety of central nervous system disorders such as parkinsonism, schizophrenia, Huntington's disease and other cognitive dysfunctions.
In parkinsonism, for example, the nigro-neostriatal hypofunction can be restored by an increase in postsynaptic DA receptor stimulation (see above)). In schizophrenia, the condition can be normalized by achieving a decrease in postsynaptic DA receptor stimulation. Classical antipsychotic agents directly block the postsynaptic DA receptor. The same effect can be achieved by inhibition of intraneuronal presynaptic events essential for the maintenance of adequate neurotransmission, transport mechanism and transmitter synthesis.
Direct DA receptor agonists, like apomorphine (a mixed DA D1/D2 agonist), are able to activate the DA autoreceptors as well as the postsynaptic DA receptors. The effects of autoreceptor stimulation appear to predominate when apomorphine is administered at low doses, whereas at higher doses the attenuation of DA transmission is outweighed by the enhancement of postsynaptic receptor stimulation. The antipsychotic and antidyskinetic effects in man of low doses of apomorphine are likely due to the autoreceptor-stimulator properties of this DA receptor agonist. This body of knowledge indicates DA receptor stimulants with a high selectivity for central nervous DA autoreceptors would be valuable in treating psychiatric disorders.
Compounds displaying preferential antagonistic effects at DA autoreceptors have been developed, Johansson et al., J. Med. Chem., 28, 1049 (1985). Examples of such compounds are (+)-cis-1S,2R-5-methoxy-1-methyl-2-(N-n-propylamino)tetralin ((+)-1S,2R-AJ76) and (+)-cis-1S,2R-5-methoxy-1-methyl-2-(N,N-di-n-propylamino)tetralin ((+)-1S,2R-UH232). Biochemically these compounds behave as classical DA antagonists, e.g. like haloperidol. Consequently, they raise the Dopa accumulation in normal animals after the blockage of aromatic amino acid decarboxylase by NSD1015 and they raise the levels of the DA metabolites DOPAC and HVA (no NSD1015 treatment). However, functionally, in behavioral testing (photocell motility meters), they display stimulatory properties, e.g. they increase the locomotor activity. In addition, gross behavioral observations show that these compounds, in certain dosages, can induce a weak classical dopaminergic stereotypic behavioral effects like sniffing and rearing in rodents.
Diseases in which an increase in dopaminergic turnover may be beneficial are geriatrics, for preventing bradykinesia and depression and in the improvement of mental functions (e.g. cognition). It can have an effect in depressed patients. It can be used in obesitas as an anorectic agent. It can improve minimal brain dysfunction (MBD), narcolepsy and negative symptoms of schizophrenia and, in addition, impotence, erectile dysfunction and restless legs. Thus, improvement of sexual functions is another indication (in both women and men).